Mutual Diffusivity of Bitumen and Liquid Hydrocarbons

Abstract

The objective of this study was to determine the mutual diffusivity for bitumen and maltenes with liquid hydrocarbons at ambient conditions. A new apparatus was designed and commissioned to measure the mass transfer in these systems based on the density profiles established over time in a column of solvent over bitumen. A one dimensional numerical model based on molecular diffusion was developed to determine the mutual diffusivity from the concentration profiles. The model accounted for the dependence of diffusivity on viscosity through a correlation based on the infinite dilution diffusivities of the solvent and the oil. Diffusivities were determined for Athabasca bitumen and maltenes with toluene, n-heptane, and n-pentane at ambient conditions and diffusion times from 3 to 15 days. The model matched the measured concentration profiles to within ±2% for bitumen and ±7% for maltenes. In addition, the effect of asphaltene precipitation of the mass transfer rate was assessed.